Plastics sorting apparatus

ABSTRACT

A conveyor ( 3 ) feeds batches of plastic chips ( 2 ) in feeding amounts W 1  to a charging device ( 4 ). After the plastic chips ( 2 ) have been stirred and charged inside the charging device ( 4 ) for a certain period of time T, they are ejected in batches and fed continuously by a screw feeder ( 20 ) to a drum electrode ( 5 ) at a feeding amount per unit time W 2 . The feeding amount per unit time W 2  is adjusted so as to satisfy W 1 /T≦W 2 ≦v×B×H×D where v is the rotation speed of the drum electrode ( 5 ), B is a width of the drum electrode ( 5 ), H is an average thickness of the plastic chips ( 2 ) that have been fed onto the drum electrode ( 5 ), and D is a bulk density of the plastic chips ( 2 ).

TECHNICAL FIELD

The present invention relates to a plastics sorting apparatus forsorting plastic chips obtained by fragmenting disposed plastic articles.

BACKGROUND ART

In recent years, the commitment to recycling garbage has been growingfast. The most common types of plastic that are consumed as raw materialfor plastic articles are vinyl chloride resin, polyethylene resin,polypropylene resin and polystyrene resin, and it seems that theyaccount for major part of disposed plastics that are collected. Torecycle such plastics, it is necessary to separate them by type.

Conventionally, a plastics sorting apparatus 50 as shown in FIG. 5 isused to sort plastic chips containing a plurality of different types ofplastics as mentioned above. This plastics sorting apparatus 50 includesa charging device 52 and an electrostatic sorting apparatus 55. Thecharging device 52 charges batches of a predetermined amount offragmented chips of different types of plastic while stirring them. Thecharged plastic chips 51 are then sorted by passing between a metal drumelectrode 53 and an electrode plate 54.

The main section 56 of the charging device 52 is provided with aninsertion portion 57 and an ejection portion 58. Inside the main section56, a stirring member 59 is provided for stirring the plastic chips 51that have been inserted into the main section 56 through the insertionportion 57. Above the insertion portion 57, a belt conveyer 60 isarranged so as to supply chips of fragmented plastic 51. The chargingdevice 52 performs batch processing, which means that after thepredetermined amount of plastic chips 51 has been stirred for a certaintime, a batch of charged plastic chips 51 is ejected from the ejectionportion 58 onto the metal drum electrode 53.

The metal drum electrode 53 is freely rotatable. Moreover, the electrodeplate 54 is fastened in opposition to the metal drum electrode 53. Ananode of a high-voltage power source 61 is connected to the metal drumelectrode 53, and a cathode of the high-voltage power source 61 isconnected to the electrode plate 54. This builds up an electrostaticfield for sorting between the metal drum electrode 53 and the electrodeplate 54. A first collecting container 62 and a second collectingcontainer 63 are arranged below the metal drum electrode 53.

The following is an explanation of how this configuration operates.

A batch of a predetermined amount of fragmented plastic chips 51 isdropped from the belt conveyor 60 into the main section 56 of thecharging device 52. Inside the main section 56, the different types ofplastic chips 51 are stirred for a certain period of time and arecharged by being rubbed against one another. The charged plastic chips51 are then ejected in batches from the ejection portion 58 of thecharging device 52 onto the peripheral surface of the rotating metaldrum electrode 53. Those plastic chips 51 that have been chargedpositively are repelled by the metal drum electrode 53 and attracted bythe electrode plate 54, and fall into the first collecting container 62.Those plastic chips 51 that have been charged negatively are attractedby the surface of the metal drum electrode 53, and fall into the secondcollecting container 63, due to the rotation of the metal drum electrode53.

While the plastic chips 51 are being stirred in the main section 56 ofthe charging device 52, no new plastic chips 51 are fed by the beltconveyor 60. After the plastic chips 51 have been stirred for a certaintime and all plastic chips 51 have been ejected from the ejectionportion 58 of the charging device 52, the next plastic chips 51 are fedfrom the belt conveyor 60 to the charging device 52.

However, in this conventional apparatus, the charging device 52 performsbatch processing, which means that after a predetermined amount ofplastic chips 51 has been stirred for a certain time, a batch of chargedplastic chips 51 is ejected. Therefore, a large amount of plastic chips51 is ejected from the charging device 52 onto the peripheral surface ofthe metal drum electrode 53 each time, and there is a danger that theplastic chips 51 accumulate on the peripheral surface of the metal drumelectrode 53 to form a layer that is thicker than is appropriate forelectro static sorting. This poses a problem that the plastic chips 51between the metal drum electrode 53 and the electrode plate 54 cannot beaccurately sorted anymore.

It is therefore an object of the present invention to provide a plasticssorting apparatus capable of adjusting the feeding amount of plasticchips during the feeding of charged plastic chips onto a movableelectrode so as to optimize the electrostatic sorting.

DISCLOSURE OF THE INVENTION

A plastics sorting apparatus in accordance with the present inventionincludes:

a charging device for charging a batch of a certain amount of differenttypes of fragmented plastic chips while stirring the plastic chips, and

an electrostatic sorting device for sorting plastic chips that have beencharged with the charging device by passing them between a pair ofsorting electrodes, characterized in that:

the charging device ejects a batch of plastic chips after stirring theplastic chips for a certain period of time T that is necessary to chargethe plastic chips;

one of the pair of sorting electrodes is a stationary electrode, and theother of the pair of sorting electrodes is a movable electrode that isarranged to oppose the stationary electrode and adapted to rotate at aperipheral speed v;

the apparatus further comprises

a first feeding device for feeding batches of a feeding amount W1 of theplastic chips to the charging device; and

a second feeding device for continuously feeding onto the movableelectrode of the electrostatic sorting device a feeding amount per unittime W2 of plastic chips that have been ejected in batches from thecharging device; and

the feeding amount per unit time W2 can be adjusted so as to satisfy

W1/T≦W2≦v×B×H×D

where B is a width of the movable electrode, H is an average thicknessof the plastic chips that have been fed onto the movable electrode, andD is a bulk density of the plastic chips.

With this configuration, the first feeding device feeds batches ofdifferent types of fragmented plastic chips in feeding amounts W1 to thecharging device, and the charging device stirs and charges the plasticchips for a certain period of time T. Then, the plastic chips areejected in batches from the charging device, fed at a feeding amount perunit time W2 by a second feeding device onto the movable electrode ofthe electrostatic sorting device, and pass between the rotating movableelectrode and the stationary electrode. By this, the plastic chips areseparated into positively charged plastic chips and negatively chargedplastic chips.

In this process for sorting the plastic chips, by satisfying W1/T≦W2,after all the batch of plastic chips that have been ejected from thecharging device are fed by the second feeding device to the movableelectrode, the next (successive) batch of plastic chips is ejected fromthe charging device and fed by the second feeding device to the movableelectrode. Thus, it can be avoided that, while first plastic chips thathave been ejected from the charging device are being fed to the movableelectrode with the second feeding device, successive plastic chips thatare ejected later are added to the first plastic chips that are still inthe second feeding device. Consequently, such a problem can be avoidedthat plastic chips pile up between the charging device and the secondfeeding device.

Moreover, by satisfying W2≦v×B×H×D, the feeding amount of plastic chipscan be set optimally for electrostatic sorting, and the plastic chipsthat have been fed to the movable electrode form a layer on the movableelectrode that has a suitable thickness for electrostatic sorting. Thus,it can be prevented that the plastic chips accumulate and form a layerthat is thicker than is appropriate for electrostatic sorting.

In accordance with the present invention, it is preferable that thecharging device includes a rotatable stirring member for stirring theplastic chips, and a feeding amount detector for detecting a feedingamount of the plastic chips that have been fed in batches from the firstfeeding device, wherein the first feeding device is a conveyor and thesecond feeding device is a screw feeder, and wherein the plasticssorting apparatus further comprising a control unit for controllingdriving devices for driving the conveyor, the stirring member, the screwfeeder and the movable electrode depending on a feeding amount that isdetected by the feeding amount detector.

With this configuration, a control device controls the driving devicessuch that W1/T≦W2≦×B×H×D is satisfied, when the feeding amount of theplastic chips that are fed in batches from the conveyor to the chargingdevice increases or decreases.

In accordance with the present invention, it is preferable that theplastics sorting apparatus further includes a shutter for opening andclosing an ejection portion of the charging device.

With this configuration, the ejection portion is closed with theshutter, while the plastic chips are being stirred inside the chargingdevice. Thus, insufficiently charged plastic chips are not ejectedinadvertently through the ejection portion. Then, after the plasticchips have been stirred for a certain period of time T, the shutteropens the ejection portion, ejecting a batch of sufficiently chargedplastic chips through the ejection portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of a plastics sortingapparatus in a configuration in accordance with the present invention;

FIG. 2 is a schematic top view of a drum electrode of the plasticssorting apparatus;

FIG. 3 is a block diagram of a control system in the plastics sortingapparatus;

FIG. 4 is a time chart illustrating how the plastics sorting apparatusis controlled; and

FIG. 5 is a diagram showing a configuration of a conventional plasticssorting apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

The following is a more detailed explanation of the present invention,with reference to the accompanying drawings (FIGS. 1 to 4).

As shown in FIGS. 1 to 3, numeral 1 denotes a plastics sorting apparatusfor sorting fragmented plastic chips 2 containing a plurality ofdifferent plastic types. This plastics sorting apparatus 1 includes acharging device 4 and an electrostatic sorting device 7.

The charging device 4 charges batches of a predetermined amount of theplastic chips 2 that have been fed by a conveyor belt 3 (example of afirst feeding device) while stirring these plastic chips 2. Theelectrostatic sorting device 7 then sorts the plastic chips 2, whichhave been charged with the charging device 4, by passing them between adrum electrode 5 (example of a movable electrode) and an electrode plate6 (example of a stationary electrode).

The belt conveyor 3, which is driven by a motor 9 (example of a drivingdevice), feeds the plastic chips 2 in batches of W1 [g] into thecharging device 4.

The charging device 4 includes a container 13 having an insertion port11 at the top and an ejection port 12 (example of an ejection portion)at the bottom, a stirring rod 14 (example of a stirring member) forstirring the plastic chips 2 that have been fed into the container 13while rotating them, a motor 15 (example of a driving device) forrotating the stirring rod 14, a shutter 16 for opening and closing theejection port 12, and a motor 17 for moving the shutter 16 so as to openand close the ejection port 12. The charging device 4 performs batchprocessing, which means that after the charging device 4 has stirred theplastic chips 2 that have been inserted into the container 13 for thetime T [sec] that is necessary for the charging, the shutter 16 opensand a batch of plastic chips 2 is ejected from the ejection port 12.

The shutter 16 is provided with a weight sensor 18 (example of a feedweight detector) for detecting the weight of plastic chips 2 that havebeen fed into the container 13. Furthermore, the certain period of timeT is measured by a timer 19. The inner volume Va [cm³] of the container13 is set to

Va≧W1/D

where D [g/cm³] is the bulk density of the plastic chips 2.

A screw feeder 20 (example of a second feeding device) is providedbetween the charging device 4 and the electrostatic sorting device 7.This screw feeder 20 continuously feeds a feeding amount per unit timeW2 [g/sec] of plastic chips 2 that have been ejected in batches from theejection port 12 of the charging device 4 on to the peripheral surfaceof the drum electrode of the electrostatic sorting device 7.

The screw feeder 20 includes a container 23 having an insertion port 21at the top on one side and an ejection port 22 at the bottom on theother side, two spiral-shaped screws 24 for transporting the plasticchips 2 that have been fed into the container 23 from the insertion port21 to the ejection port 22 while rotating them, and a motor 25 (exampleof a driving means) for rotating the screws 24. The two screws 24 arearranged in parallel inside the container 23.

A funnel-shaped buffer 26, whose lower aperture becomes graduallynarrower than its upper aperture, is arranged between the ejection port12 of the charging device 4 and the insertion port 21 of the screwfeeder 20. The inner volume Va of this buffer 26 is chosen to be atleast the inner volume of the container 13 of the charging device 4.

The drum electrode 5 is a cylindrical member made of metal, which isrotated by a motor 28 (example of a driving device) at a peripheralspeed v [cm/sec] in a constant direction around its horizontal axis. Thedrum electrode 5 has the width B [cm] in the direction of the horizontalaxis, as shown in FIG. 2. The electrode plate 6 is fastened at a certaininterval in opposition to the peripheral surface of the drum electrode5. A high-voltage dc power source 29 applies a high voltage between thedrum electrode 5 and the electrode plate 6. The cathode of thehigh-voltage dc power source 29 is connected to a current-supply brush30 wiping along the peripheral surface of the drum electrode 5. Thecathode of the high-voltage dc power source 29 is connected to theelectrode plate 6. Thus, the drum electrode 5 is charged positively,whereas the electrode plate 6 is charged negatively.

Below the drum electrode 5, a first collecting container 31 and a secondcollecting container 32 are arranged for collecting the different typesof plastic chips 2, which have been sorted by passing between the drumelectrode 5 and the electrode plate 6. Moreover, a scraper 33 forscraping off plastic chips 2 that adhere to the peripheral surface ofthe drum electrode 5 is arranged at the periphery of the drum electrode5.

The feeding amount per unit time W2 [g/sec] that is fed by the screwfeeder 20 is adjusted so as to satisfy

W1/T≦W2≦v×B×H×D  (1)

where H [cm] is the average thickness of the layer of plastic chips 2that is fed from the screw feeder 20 to the peripheral surface of thedrum electrode 5.

As shown in FIG. 3, the plastics sorting apparatus 1 is also providedwith a control device 35 for controlling the motors 9, 15, 17, 25 and 28such that Equation (1) is satisfied, in accordance with the weight ofplastic chips 2 that is detected by the weight sensor 18 and the timethat is measured by the timer 19.

The following is an explanation of the operation of this configuration.

First of all, the belt conveyor 3, which is driven by the motor 9, feedsa feeding amount W1of different types of fragmented plastic chips 2 inbatches through the insertion port 11 of the charging device 4 into thecontainer 13.

Then, the weight sensor 18 detects the weight of the feeding amount W1of plastic chips 2 that have been fed into the container 13, and theplastic chips 2 are stirred by rotating the stirring rod 14 with themotor 15. The stirring is performed for a certain period of time T thatis taken with the timer 19, and causes the different kinds of plasticchips 2 to rub against one another, whereby the plastic chips 2 arecharged.

After the certain period of time T has elapsed, the rotation of thestirring rod 14 is halted, the motor 17 opens the shutter 16, asindicated by the dash-dotted line in FIG. 1, there by opening theejection port 12 of the charging device 4, and a batch of plastic chips2 is ejected from the ejection port 12, passes the buffer 26, and isinserted through the insertion port 21 of the screw feeder 20 into thecontainer 23.

Thus, the plastic chips 2 that have been inserted into the screw feeder20 are transported by the two screws 24, which are rotated by the motor25, from the insertion port 21 through the container 23 towards theejection port 22, and the feeding amount per unit time W2 is fedcontinuously from the ejection port 22 to the peripheral surface of thedrum electrode 5.

Because the drum electrode 5 rotates at the peripheral speed v, theplastic chips 2 pass between the drum electrode 5 and the electrodeplate 6. At this moment, plastic chips 2 that have been chargedpositively are repelled by the drum electrode 5 and attracted by theelectrode plate 6 and fall into the first collecting container 31. Onthe other hand, plastic chips 2 that have been charged negatively areattracted by the drum electrode 5 and fall into the second collectingcontainer 32. Thus, the plastic chips 2 are sorted.

In this process for sorting the plastic chips 2, by satisfying W1/T≦W2 ,after a batch of plastic chips 2 has been fed by the screw feeder 20from the charging device 4 to the drum electrode 5, the next batch ofplastic chips 2 is ejected from the charging device 4 and fed by thescrew feeder 20 to the drum electrode 5. Thus, it can be avoided thatwhile first plastic chips 2 that have been ejected from the chargingdevice 4 are being fed to the drum electrode 5 with the screw feeder 20,successive plastic chips 2 that are ejected later and inserted into thescrew feeder 20, are added to the first plastic chips 2 that are stillin the screw feeder 20. Consequently, the problem can be avoided thatplastic chips 2 pile up between the charging device 4 and the screwfeeder 20.

Moreover, by satisfying W2≦v×B×H×D, the feeding amount per unit time W2of plastic chips 2 can be set optimally for electrostatic sorting, andthe plastic chips 2 that have been fed to the drum electrode 5 form alayer on the peripheral surface of the drum electrode 5 that is thinenough for electrostatic sorting. Thus, it can be prevented that theplastic chips 2 accumulate to a form a layer that is thicker than isappropriate for electrostatic sorting, so that the plastic chips 2 canbe reliably electrostatically sorted.

The control device 35 controls the motors 9, 15, 17, 25 and 28 so as tosatisfy Equation (1). For example, when the feeding amount W1of plasticchips 2 fed in batches from the belt conveyor 3 to the charging device 4is increased to sort large amounts of plastic chips 2, the weight of theplastic chips 2 that is detected by the weight sensor 18 increases aswell, so that the control device 35 increases the rotation speeds of themotors 25 and 28 in accordance with the detected weight. This increasesthe rotation speed of the screws 24 of the screw feeder 20, so that thefeeding amount per unit time W2 from the screw feeder 20 to the drumelectrode 5 increases, the peripheral speed v of the drum electrode 5increases, and the Equation (1) is satisfied. Conversely, when thefeeding amount W1 is decreased, the opposite control is performed.

FIG. 4 is a time chart showing the control during this sorting process.When the sorting starts, the motor 9 is turned on and drives the beltconveyor 3 for a certain period of time t, whereby a batch of plasticchips 2 is inserted into the container 13 of the charging device 4.Then, the weight sensor 18 and the motor 15 are turned on, rotating thestirring rod 14. Then, after a predetermined time T has elapsed, themotor 15 is turned off, the stirring rod 14 is halted, whereas the motor17 is turned on to open the shutter 16 for a certain period of time.This ejects a batch of plastic chips 2 from the charging device 4,thereby turning the weight sensor 18 off. The motor 25 of the screwfeeder 20 and the motor 28 of the electrostatic sorting device 7 areboth turned on at the beginning of the sorting process, when the motor 9of the belt conveyor 3 is turned on, and the screw 24 and the drumelectrode 5 rotate continuously until the sorting is finished.

The following illustrates an example using the numerical values listedbelow for Equation (1):

Bulk density D of the plastic chips 2; D=0.4 g/cm³

Diameter Φ of the drum electrode 5; Φ=50 cm

Width B of the drum electrode 5; B=100 cm

Rotation speed of the drum electrode 5 per minute;=20 rpm

Average thickness H of layer of plastic chips 2; H=0.05 cm

Period of time T necessary for charging the plastic chips 2; T=30 sec

Feeding amount W1 of plastic chips 2 fed by the conveyor belt 3; W1=7.5liter=7.5×10³×0.4 g=3×10³ g

Feeding amount per unit time W2 of plastic chips 2 fed by the screwfeeder 20; W2=100 g/sec Here, the peripheral speed v of the drumelectrode 5 is v=50 cm×π×20 rpm/60=52.3 cm/sec

Insertion of these values into Equation (1) yields;

3×10³ g/30 sec≦100 g/sec≦52.3 cm/sec×100 cm×0.05 cm ×0.4 g/cm³

Thus, W2 satisfies Equation (1):

W1/T (=100)≦W2 (=100)≦v×B×H×D (=104.6)

In the above-described embodiment, the ejection port 12 of the chargingdevice 4 is opened with the shutter 16. Therefore, while the plasticchips 2 are stirred inside the charging device 4, insufficiently chargedplastic chips 2 can be prevented from being ejected inadvertentlythrough the ejection port 12 by keeping the ejection port 12 closed withthe shutter 16. Then, after the plastic chips 2 have been stirred for acertain period of time T, the shutter 16 opens the ejection port 12,ejecting a batch of sufficiently charged plastic chips 2 through theejection port 12.

In the above-described embodiment, plastic chips 2 that adhere to theperipheral surface of the drum electrode 5 and have not fallen down arescraped off with the scraper 33, and collected in the second collectingcontainer 32.

In the above-described embodiment, a belt conveyor 3 is used as anexample of a first feeding device. However, it is also possible to usetransport dollies or the like to transport the plastic chips 2 to aposition above the insertion port 11 of the charging device 4, and thendrop the plastic chips 2 into the insertion port 11.

In the above-described embodiment, a biaxial screw feeder 20 having twoparallel screws 24 is used as an example of a second feeding device.However, it is also possible to provide only one or three or more screws24, depending on the width B of the drum electrode 5. Moreover, insteadof a screw feeder 20, it is also possible to use a belt conveyor or arotary valve to feed the plastic chips 2 in desired quantities.

In the above-described embodiment, the drum electrode 5 is chargedpositively, whereas the electrode plate 6 is charged negatively, but itis also possible to use reverse polarities for the charging.

In the above-described embodiment, a rotatable stirring rod 14 isprovided inside the container 13 of the charging device 4 as an exampleof a stirring member. However, the present invention is not limited torod shapes, and wing shapes can be used as well. In addition, it is alsopossible to stir the plastic chips 2 by rotating the container 13 with amotor.

In the above-described embodiment, the plastic chips 2 are charged bystirring them by rotating the stirring rod 14 for a predetermined timeT. However, it is also possible to charge the plastic chips 2 byirradiation with ions for a predetermined time T.

INDUSTRIAL APPLICABILITY

The plastics sorting apparatus in accordance with the present inventionas described above is suitable for sorting plastic chips by type, thathave been obtained by fragmenting disposed plastic articles.

What is claimed is:
 1. A plastics sorting apparatus comprising: acharging device for charging a batch of a predetermined amount ofdifferent types of fragmented plastic chips while stirring the plasticchips; and an electrostatic sorting device for sorting plastic chipsthat have been charged with the charging device by passing them betweena pair of sorting electrodes, characterized in that: the charging deviceejects a batch of plastic chips after stirring the plastic chips for acertain period of time T that is necessary to charge the plastic chips;one of the pair of sorting electrodes is a stationary electrode, and theother of the pair of sorting electrodes is a movable electrode that isarranged to oppose the stationary electrode and adapted to rotate at aperipheral speed v; the apparatus further comprises a first feedingdevice for feeding batches of a feeding amount W1 of the plastic chipsto the charging device, and a second feeding device for continuouslyfeeding onto the movable electrode of the electrostatic sorting device afeeding amount per unit time W2 of the plastic chips that have beenejected in batches from the charging device; and the feeding amount perunit time W2 is set to satisfy W1/T≦W2≦v×B×H×D where B is a width of themovable electrode, H is an average thickness of the plastic chips thathave been fed onto the movable electrode, and D is a bulk density of theplastic chips.
 2. The plastics sorting apparatus as set forth in claim1, wherein the charging device comprises a rotatable stirring member forstirring the plastic chips, and a feeding amount detector for detectinga feeding amount of the plastic chips that have been fed in batches fromthe first feeding device; wherein the first feeding device is a conveyorand the second feeding device is a screw feeder; and wherein theplastics sorting apparatus further comprises a control unit forcontrolling driving devices for driving the conveyor, the stirringmember, the screw feeder and the movable electrode depending on thefeeding amount that is detected by the feeding amount detector.
 3. Theplastics sorting apparatus as set forth in claim 1, further comprising ashutter for opening and closing an ejection portion of the chargingdevice.
 4. The plastics sorting apparatus as set forth in claim 2,further comprising a shutter for opening and closing an ejection portionof the charging device.